It is known that organic materials such as thermoplastic resins, thermosetting resins, crystalline resins, amorphous resins, biodegradable resins, non-biodegradable resins, engineering resins, polymer alloys, natural and synthetic rubbers, lubricating oils, adhesives and paints undergo molecular cleavage and/or molecular cross-linking when subjected to the effect of heat, oxygen, light and the like and this is accompanied by reduction in the strength and physical properties of the organic materials as well as deterioration of the outer appearance due to coloration and the like, so that their commercial values are markedly impaired. In order to solve this problem, organic materials are stabilized by using them in combination with a variety of stabilizers, such as phenolic antioxidants, phosphorus-based antioxidants, thioether-based antioxidants, lactone-based stabilizers, hydroxylamine-based antioxidants, vitamin E-based antioxidants, hindered amine-based stabilizers and ultraviolet absorbers.
Among these stabilizers, phosphorus-based antioxidants are widely used because they not only show excellent deterioration-inhibiting effect particularly during processing and are capable of exerting a synergistic effect with other stabilizers but also can be applied to almost any resin that is used as a plastic material. As phosphorus-based antioxidants, compounds of various structures are utilized; however, there are cases where a unique phosphite odor is generated with time when such compounds are exposed to a high temperature or stored over a long period. An addition of an odor-generating phosphorus-based antioxidant to a resin may result in the generation of an unpleasant odor during molding of the resin and/or the generation of an odor in the resulting molded article.
There have been made a number of reports on investigation relating to improvement in the odor of molded articles and, for example, Patent Document 1 proposes the use of a phosphite compound having a melting point of higher than 40° C. in a fatty acid cellulose ester-based resin composition. In Patent Document 2, it is proposed to incorporate a phenolic antioxidant and a phosphite compound for the purpose of improving the odor of an epoxidized vegetable oil composition. Further, in Patent Document 3, it is proposed to incorporate an organic carboxylic acid zinc salt and an alkyl phosphite compound for the purpose of improving the odor that is generated when an epoxidized vegetable oil is added to a vinyl chloride resin composition.
Moreover, in Patent Document 4, for the purpose of improving the odor that is generated when water is allowed to pass through a hose made of a vinyl chloride-based resin, it is proposed to incorporate a phosphorus-based antioxidant, such as trisnonylphenyl phosphite or tris(2,4-di-tert-butylphenyephosphite, into a vinyl chloride-based resin composition. Furthermore, in Patent Document 5, for the purpose of improving the odor of a metallocene-based polyethylene, it is proposed to incorporate a phenolic antioxidant and a phosphorus-based stabilizer, such as tris(2,4-di-tert-butylphenyl)phosphite or (2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, into a resin composition.